Traditionally, when refrigerant charged refrigeration systems were repaired, the refrigerant charge was simply loosed to the atmosphere as necessary to accomplish the repairs. In recent times, it has become increasingly desirable to capture and reuse the refrigerant charge in these units for two reasons; refrigerant pollution of the atmosphere is perceived as environmentally destructive and the cost of refrigerant materials has increased making the disposal and replacement of a refrigerant charge increasingly unacceptable and costly.
Refrigerant recovery devices are known in the art which compress and cool refrigerant taken from a charged refrigeration system to a liquid state for storage in a refrigerant storage container and later reintroduction to the same refrigeration system after repair has been accomplished or for use in another system. Many of these recovery systems filter the refrigerant during the removal-compression-cooling process to remove contaminants from the recovered refrigerant before it is introduced into a storage container. However, these devices typically have not provided for effective removal of "incompressible" gas contaminants, i.e. gasses much less compressible than the refrigerant, such as air, from the used refrigerant during the recovery process before it is introduced into a storage container. Thus, incompressible contaminate gases frequently remain in solution in the liquid phase refrigerant when it is introduced into the storage container and must be purged off from the storage container over time using a time-temperature-pressure method to make the recovered refrigerant acceptable for reuse.
A frequently used method for purging incompressible contaminants from recovered refrigerant is well known, and Underwriters Laboratories, Inc. requires that a description of the method and vapor-pressure-temperature charts for various common refrigerants required to implement it, be provided in operator manuals for recovery equipment certified by it. Generally, the method of purging incompressible contaminant gases from a known type of refrigerant in a storage container involves the steps of determining the temperature of the stored refrigerant, measuring the pressure of the refrigerant in the container and comparing that pressure to a pressure determined from a temperature-vapor-pressure chart for pure refrigerant of that type. If the pressure of the refrigerant in the container is significantly higher than the pressure shown on the chart for pure refrigerant of that type at that temperature, for example, five psi. higher, the storage tank is briefly vented at the top to release lighter incompressible gasses which have accumulated in the top of the container. For example, a 50 pound storage container may be vented for about five seconds. After venting, the storage vessel may be tamped to accelerate the release of incompressible contaminants from dissolution in the liquid phase stored refrigerant. The storage vessel is then allowed to stand for a period of time, and the process is repeated until the pressure is within an acceptable range of that of pure refrigerant at the determined temperature.
During the process, the pressure of the stored refrigerant may be determined by attaching a pressure gauge to the storage tank. Alternatively, in the case of refrigerant recovery machinery provided with a gauge indicating the pressure of refrigerant at the outlet by which the machine is connected to a storage tank, the tank may be left connected, or may be reconnected, to the refrigerant recovery device and the pressure determined from that gauge.
Heretofore, the temperature of refrigerant within the storage container has been determined in a number of ways. Some refrigerant recovery machines of the prior art are equipped with temperature gages indicating the temperature of refrigerant gas in the machine at a point proximate to the outlet pressure gauge discussed above. Generally, however, recovery machines are attached to a storage vessel by a length of tube or hose, and the temperature at such a temperature gauge will not accurately reflect that of refrigerant in the storage container. Further, as in the case of using recovery machine gauges to measure pressure of refrigerant in the container, this method requires the availability of the recovery machine, tieing-up a machine which might otherwise be profitably employed in recovery operations. Alternatively, the storage container may be left to stand for a period of time after filling, and, the refrigerant then assumed to be at ambient temperature. This method requires a storage location with a known and constant ambient temperature, and, a substantial period of time may be required for the refrigerant in the storage vessel to cool to ambient temperature after being filled by a refrigerant recovery machinery. Also, hand-held temperature sensing devices such as, for example, digital pyrometers, have been utilized to measure the temperature of stored recovered refrigerant by bringing a temperature-sensing of stored recovered refrigerant by bringing a temperature-sensing probe into contact with the storage tank to determine its temperature. This method requires the inconvenience, expense and maintenance of an additional tool.
Temperature-pressure charts from which a vapor pressure corresponding to refrigerant temperature may be determined for various types of pure refrigerant are generally provided in operator manuals for refrigeration recovery machinery or on cards to be carried by machine operators. Thus, an operator manual or vapor-pressure-temperature chart card must be made available at the location of the storage container.